1. Field of the Invention
The present invention relates in general to a vibration-isolating laminar rubber structure, and more particularly to a vibration-isolating laminar rubber structure suitably used as an elastic support or cushioning body for supporting a civil engineering structure or a building or architectural structure, in a vibration isolating or damping fashion. For instance, the laminar rubber structure is suitably used as a support interposed between a beam and a pier of a bridge.
2. Discussion of the Related Art
There has been known a vibration-isolating elastic support or cushioning body in the form of a laminar rubber structure used for supporting a structure in the fields of civil engineering and building or architectural construction. Such a laminar rubber structure is interposed between an upper structure and a lower structure. Since the upper structure to be supported by the laminar rubber structure usually has a considerably large weight, the laminar rubber structure is constructed to include metal plates or other hard plates having a high degree of rigidity, such that the hard plates and rubber layers are alternately laminated on each other to constitute a laminar structure, which is highly capable of functioning as an elastic support or cushioning body for supporting a building or architectural structure, or a bridge pier or other civil engineering structure, in a vibration damping or isolating manner.
Described in detail by reference to FIG. 1, a vibration-isolating laminar rubber structure 10 shown therein by way of example includes a rubber block 12 wherein a plurality of hard plates in the form of metal plates 14 are embedded in parallel with each other such that the metal plates 14 are spaced apart from each other at a predetermined spacing interval, so that the metal plates 14 and rubber layers 16 are alternately arranged to provide the rubber block 12 in the form of an integral laminar body. The laminar rubber structure 10 further includes an upper mounting plate 18 and a lower mounting plate 20, which are both formed of a metallic material and secured to the respective upper and lower end faces of the rubber block 12. The laminar rubber structure 10 is interposed between an upper structure such as a beam of a bridge and a lower structure such as a pier of the bridge, such that the laminar rubber structure 10 is fixed at the upper and lower mounting plates 18, 20 to the beam and pier of the bridge, respectively. The laminar rubber structure 10 is capable of supporting a relatively large weight of the upper structure such as a concrete bridge beam having a large weight, in a vibration damping or isolating fashion. The laminar rubber structure 10 exhibits a damping or cushioning effect in a shearing direction, for absorbing or accommodating deflection, flexure or displacement of the bridge beam which may be caused by an earthquake, a strong wind, or a weight or acceleration of vehicles running on the bridge. The laminar rubber structure 10 also exhibits a damping or cushioning effect for absorbing or damping a vibrational load which acts on the bridge beam in the vertical direction.
It will be understood that the vibration-isolating laminar rubber structure constructed as described above desirably is required to exhibit not only a high vibration isolating, damping or absorbing effect, but also a low dependency of its modulus of elasticity on the temperature. Generally, the laminar rubber structure is used at a temperature which varies over a relatively wide range, Where the laminar rubber structure is used for supporting a bridge beam on a pier, the laminar rubber structure is usually placed in a severe natural environment, being exposed to a below-freezing temperature up to a temperature far exceeding 30.degree. C.
However, the rubber layers in the rubber block provided in the conventional vibration-isolating laminar rubber structure are formed of an ordinary rubber composition which is a mixture of a rubber material such as a natural rubber (NR) and a suitable vulcanizing agent. Such an ordinary rubber composition is not satisfactory in its vibration isolating or damping properties. Further, the inclusion of known components conventionally used to improve the isolating or damping properties causes an undesirable increase in the temperature dependency of the modulus of elasticity of the rubber layers, namely, undesirable deterioration of its elastic characteristics of the laminar rubber structure as a whole, due to a considerable influence by the ambient temperature.